OK then.
Old poster found in a closet in a Jewish preschool where redditor noramorse says she/he was a teacher. I don't believe this is an official ad via the National Watermelon Growers of America.
The watermelon poster is a response to the above ad for Levy's Jewish rye bread, one execution from a well-known 1960s ad campaign created by the New York City ad agency Doyle Dane Bernbach. Here's more of the campaign.
Looks like they got the typeface correct.
